INTRODUCTION: Placental pathology is an important contributor in preterm birth, both spontaneous and indicated. The aim of this study was to describe and compare placental histological features of spontaneous preterm birth versus indicated preterm birth. METHODS: A case control study was performed at the University Medical Center Utrecht. Women with spontaneous or indicated preterm birth (17-37 weeks of gestation) delivered in 2009 were included. Women with a pregnancy complicated by congenital and/or chromosomal abnormalities were excluded. Placentas were systematically examined by an expert pathologist blinded for pregnancy outcome, except for gestational age. Placental histological abnormalities were classified into infectious inflammatory lesions and maternal vascular malperfusion lesions and compared between spontaneous and indicated preterm birth. Analysis was stratified for immature (17-23(+6) weeks), extremely (24-27(+6) weeks), very (28-31(+6) weeks) and moderate/late (32-36(+6) weeks) preterm birth. RESULTS: We included 233 women, 121 women with spontaneous preterm birth and 112 women with indicated preterm birth. Among women with spontaneous extremely preterm birth, higher rates of severe chorioamnionitis were found (56.0% vs. 0%). Furthermore, a shift from infectious-inflammatory lesions to maternal vascular malperfusion lesions was seen after 28 weeks; in women with spontaneous very and moderate/late preterm birth, maternal vascular malperfusion lesions were the main finding (46.8% and 47.7% respectively). In women with indicated preterm birth, maternal vascular malperfusion lesions were most often contributing through all gestational age categories. CONCLUSION: Maternal vascular malperfusion lesions are most frequent in both spontaneous and indicated very and moderate/late preterm birth. In spontaneous extreme preterm birth chorioamnionitis is the main finding.